Imaging of z~2 QSO Host Galaxies with the Hubble Space Telescope

Abstract

We report on deep imaging in two filters with the planetary camera of the Hubble Space Telescope of five QSOs at redshift of ~2, with a range of optical and radio luminosity. The observations included a suite of point-spread function (PSF) observations that were used to construct new PSF models, described elsewhere by Dumont et al. The new PSF models were used to remove the QSO nucleus from the images. We find that the host galaxies have resolved flux of the order of 10% of the QSO nuclei and are generally luminous and blue, indicating active star formation. While most have clearly irregular morphologies, the bulk of the flux can be modeled approximately by an R^1/4 law. However, all host galaxies also have an additional approximately exponential luminosity profile beyond a radius of about 0.8", as also seen in ground-based data with larger telescopes. The QSOs all have a number of nearby faint blue companions that may be young galaxies at the QSO redshift. We discuss implications for evolution of the host galaxies, their spheroidal populations, and central black holes. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.